Why does my roof only leak in heavy rain?

When a residential roof only leaks during heavy downpours rather than light drizzles, it usually means that the volume of water exceeds the capacity of minor structural defects or compromised drainage channels to handle it safely. During light rain, water evaporates or flows slowly through minor gaps without penetrating the interior. In heavy rain, overwhelmed gutters overflow backward under eaves, or large volumes of water rapidly bypass flashing seals around chimneys and vents, pouring into the attic. You can troubleshoot heavy rain leaks safely by tracing water stains upward in your attic. You can verify that your corrective action is successful when sealing flashing joints, clearing blocked gutters, and repairing damaged roof valleys ensures the system handles high-volume downpours without interior leaks.